Electroconvulsive therapy (ECT) has unparalleled efficacy in treating severe depression that is resistant to common modalities of treatment, such as antidepressant medication. Although treatment with ECT has benefited many individuals with treatment resistant depression (rates as high as 50-75%), its more widespread use is hindered by the social stigma associated with the treatment, as well as by its significant cognitive side effects. Moreover, ECT cannot be precisely targeted, since it produces a widespread activation of the brain surface, in turn, affecting many different functional areas. Magnetic seizure therapy (MST) is currently being investigated as an alternative to ECT, as it is more focused to one area of the brain. Rather than applying electrical stimuli to induce a seizure, as is done in ECT, MST uses repetitive magnetic stimulation to produce the seizure. Preliminary research suggests that MST can result in therapeutic effects comparable to those produced by ECT, but without the negative side effects on cognition. The proposed study is a randomized, controlled trial, in which the efficacy and side effect profile of MST will be compared to those of ECT. If successful, the results of this study may lead to increased treatment availability and accessibility, as well as lessen the substantial health care costs associated with treatment resistant depression.